Method for producing feedstocks of high quality lube base oil from unconverted oil

ABSTRACT

The present invention relates to a method of producing a feedstock for high-quality lube base oil from unconverted oil (UCO) obtained from fuel oil hydrocracking, and more particularly to a method of producing a feedstock for high-quality lube base oil by treating vacuum gas oil (VGO) or a mixture of vacuum gas oil (VGO) with coker gas oil (CGO) or deasphalted oil (NAO) as a feedstock in a hydrotreating unit and a first hydrocracking unit and recycling the resulting unconverted oil (UCO) through a second hydrocracking unit.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.10-2007-0084507, filed Aug. 22, 2007, entitled “Method for producingfeedstocks of high quality lube base oil from unconverted oil”, which ishereby incorporated by reference in its entirety into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of producing a feedstock forhigh-quality lube base oil from unconverted oil (UCO) obtained from fueloil hydrocracking, and more particularly to a method of producing afeedstock for high-quality lube base oil by hydrotreating vacuum gas oil(VGO) or a mixture of vacuum gas oil (VGO) with coker gas oil (CGO) ordeasphalted oil (DAO) as a feedstock in a hydrotreating unit and a firsthydrocracking unit and recycling the resulting unconverted oil (UCO)through a second hydrocracking unit.

2. Description of the Prior Art

A process of producing a feedstock for high-quality lube base oilthrough a fuel oil hydrocracking process is a method of usingunconverted oil (UCO), which is generated during the hydrocracking ofvacuum gas oil (VGO) produced in a vacuum distillation unit (V1). Inthis method, the VGO is first fed into a hydrotreating (HDT) unit toremove sulfur, nitrogen, oxygen and metals from the VGO, and then asignificant amount of the hydrotreated VGO is converted to lighthydrocarbons through a hydrocracking (HDC) process, which is a mainreaction process. The light hydrocarbons are passed through a series offractionators (Fs) to separate various oils and gases therefrom, thusproducing light oil products.

In the reaction, the pass conversion is generally designed to be about40%, and it is impossible in practice to accomplish a pass conversion of100%. For this reason, unconverted oil (UCO) is always generated in thefractionators, and a portion of the unconverted oil is drawn to theoutside for use as a feedstock for lube base oil, and the remainingunconverted oil is recycled to the hydrocracking unit.

Aromatic compounds, sulfur compounds, oxygen compounds and nitrogencompounds, which are contained in the vacuum gas oil (VGO) feed in largeamounts, are almost all saturated with hydrogen through thehydrotreating process. For this reason, more than 90% of the unconvertedoil (UCO) byproducts are saturated hydrocarbons, and thus have a highviscosity index, which is one of the most important properties for lubebase oil.

The applicant suggested an effective method of producing feedstocks forfuel oil and high-quality lube base oil, in which unconverted oil (UCO)is drawn out directly during the recycle mode operation of the vacuumgas oil (VGO) hydrocracking unit to provide a feedstock for producinglube base oil, such that the loads on a first vacuum distillation unit(V1; a process for vacuum distillation of atmospheric residue) andhydrotreating and hydrocracking units (R1 and R2) are reduced withoutthe need to recycle the VGO to the first vacuum distillation process(V1) (Korean Patent Publication No. 96-13606). In this method, 100N- and150N-grade feedstocks for high-quality lube base oils could be producedat greatly reduced inefficiency, but the method was designed to use onlyvacuum gas oil (VGO), and did not consider producing a feedstock forhigh-quality lube base oil in a more economic manner by recyclingunconverted oil (UCO) using, in addition to vacuum gas oil, coker gasoil (CGO) or deasphalted oil (DAO), which are inexpensive and, at thesame time, have a high concentration of impurities and low oxidationstability. Also, the method had shortcomings in that, because thehydrocracking unit consisted simply of a single stage, the size of therequired reactor was increased, and in addition, the operating cost wasincreased due to the severity of operating conditions.

SUMMARY OF THE INVENTION

Accordingly, the applicant has conducted many studies to maximize theefficiency and economy of the above-described method for producing afeedstock for high-quality lube base oil and, as a result, has developeda method capable of effectively producing a feedstock for high-qualitylube base oil by recycling unconverted oil, generated from thehydrotreating and hydrocracking of either vacuum gas oil or a mixture ofvacuum gas oil with coker gas oil (CGO) or deasphalted oil (DAO),through a second hydrocracking process.

Therefore, the present invention provides a method for producing afeedstock for high-quality lube base oil, which can maximize efficiencyby recycling unconverted oil (UCO) of an oil hydrocracking unit througha second hydrocracking unit and, at the same time, can remarkablyimprove economic efficiency by employing coker gas oil (CGO) ordeasphalted oil (DAO), which is otherwise not very useful.

In one aspect, the present invention provides a method of producing afeedstock for high-quality lube base oil from unconverted oil, themethod including: distilling atmospheric residue (AR) in a first vacuumdistillation unit (V1) to obtain vacuum gas oil (VGO), and feeding thevacuum gas oil (VGO) into a hydrotreating unit (HDT); removingimpurities from the vacuum gas oil through the hydrotreating unit (HDT);obtaining light and heavy hydrocarbons from the vacuum gas oil through afirst hydrocracking unit (HDC1); feeding the light and heavyhydrocarbons into fractionators (Fs) to separate the hydrocarbons intooil products and unconverted oil; feeding a portion of the separatedunconverted oil into a second vacuum distillation unit (V2) to obtain afeedstock for high-quality lube base oil, having a given viscositygrade, and the remaining unconverted oil; feeding the remainingunconverted oil, separated from the fractionators (Fs), and theunconverted oil, obtained from the second vacuum distillation unit (V2),into a second hydrocracking unit (HDC2); and recycling light and heavyhydrocarbons, obtained through the second hydrocracking process (HDC2),to the fractionators (Fs).

In another aspect, the present invention provides a method of producinga feedstock for high-quality lube base oil from unconverted oil, themethod including: distilling atmospheric residue (AR) in a first vacuumdistillation unit (V1) to separate it into vacuum gas oil (VGO) andvacuum residue (VR) or a mixture of atmospheric residue (AR) with vacuumresidue (VR), feeding the vacuum gas oil (VGO) directly into ahydrotreating (HDT) unit, feeding the vacuum residue (VR) or the vacuumresidue/atmospheric residue mixture (VR/AR) through fractionators (Fs)to coker drums to subject it to a coking process and passing the cokedresidue through fractionators (Fs′) to obtain coker gas oil, and feedingthe obtained coker gas oil together with the vacuum gas oil (VGO) into ahydrotreating (HDT) unit; removing impurities from the vacuum gas oiland the coker gas oil through the hydrotreating (HDT) unit; obtaininglight and heavy hydrocarbons from the vacuum gas oil through a firsthydrocracking (HDC1) unit; feeding the light and heavy hydrocarbons intofractionators (Fs) to separate the hydrocarbons into oil products andunconverted oil; feeding a portion of the unconverted oil to a secondvacuum distillation unit (V2) to obtain a feedstock for high-qualitylube base oil, having a given viscosity grade, and the remainingunconverted oil; feeding the remaining unconverted oil, separated fromthe fractionators, and the unconverted oil, obtained from the secondvacuum distillation unit (V2), into a second hydrocracking unit (HDC2);and recycling light and heavy hydrocarbons, obtained through the secondhydrocracking unit (HDC2), to the fractionators.

In still another aspect, the present invention provides a method ofproducing a feedstock for high-quality lube base oil from unconvertedoil, the method including: distilling atmospheric residue in a firstvacuum distillation unit (V1) to separate it into vacuum gas oil (VGO)and vacuum residue (VR), feeding the vacuum gas oil (VGO) directly intoa hydrotreating unit (HDT), feeding the vacuum residue into a solventdeasphalting unit (SDA) to obtain deasphalted oil (DAO) from whichasphalt and impurities have been removed, and feeding the deasphaltedoil (DAO) together with the vacuum gas oil (VGO) into the hydrotreatingunit (HDT); removing impurities from the vacuum gas oil and thedeasphalted oil through the hydrotreating unit (HDT); obtaining lightand heavy hydrocarbons from the vacuum gas oil and the deasphalted oilthrough a first hydrocracking unit (HDC1); feeding the light and heavyhydrocarbons into fractionators (Fs) to separate the hydrocarbons intooil products and unconverted oil; feeding a portion of the separatedunconverted oil to a second vacuum distillation unit (V2) to obtain afeedstock for high-quality lube base oil, having a given viscositygrade, and the remaining unconverted oil; feeding the remainingunconverted oil, separated from the fractionators, and the unconvertedoil, obtained from the second vacuum distillation unit (V2), into asecond hydrocracking unit (HDC2); and recycling light and heavyhydrocarbons, obtained through the second hydrocracking unit (HDC2), tothe fractionators (Fs).

According to the present invention, the feedstock for high-quality lubebase oil can be produced in a more efficient manner by carrying out thehydrotreating (HDT) process and the first hydrocracking (HDC1) processusing vacuum gas oil (VGO) or the mixture of vacuum gas oil (VGO) withcoker gas oil (CGO) or deasphalted oil (DAO) as a feedstock, andrecycling the unconverted oil, obtained from the first hydrocrackingunit, to the second hydrocracking unit (HDC2). Also, a high-value-addedfeedstock for high-quality lube base oil can be produced in a moreeconomical manner through the use of coker gas oil (CGO) and deasphaltedoil (DAO), which have a low grade and are difficult to treat.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a schematic process diagram of an embodiment of the presentinvention, in which a feedstock for high-quality lube base oil isproduced in a fuel oil hydrocracking process in a recycle-mode operationusing vacuum gas oil as a feedstock;

FIG. 2 is a schematic process diagram of an embodiment of the presentinvention, in which a feedstock for high-quality lube base oil isproduced in a fuel oil hydrocracking process in a recycle-mode operationusing a mixture of vacuum gas oil and coker gas oil as a feedstock; and

FIG. 3 is a schematic process diagram of an embodiment of the presentinvention, in which a feedstock for high-quality lube base oil isproduced in a fuel oil hydrocracking process in a recycle-mode operationusing a mixture of vacuum gas oil and deasphalted oil as a feedstock.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described in detail withreference to the accompanying drawings.

FIG. 1 is a schematic process diagram of an embodiment of the presentinvention, in which a feedstock for high-quality lube base oil isproduced in a fuel oil hydrocracking process in a recycle-mode operationusing vacuum gas oil (VGO) as a feedstock. As shown in FIG. 1, vacuumgas oil (VGO) produced from a first vacuum distillation unit (V1) is fedinto a hydrotreating unit (HDT) to remove impurities, including sulfur,nitrogen, oxygen and metal components, from the vacuum gas oil (VGO),and a light oil fraction is produced from the hydrotreated vacuum gasoil through a first hydrocracking unit (HDC1). Also, unconverted oil(UCO), obtained from the first hydrocracking unit (HDC1), is fed into asecond hydrocracking unit (HDC2) and recycled, thus producing afeedstock for high-quality lube base oil.

Unlike the prior single-stage hydrocracking process, in the presentinvention, the unconverted oil, obtained by passing the vacuum gas oilthrough the single-stage hydrotreating unit (HDT) and the firsthydrocracking unit (HDC) and then passing the hydrocracked vacuum gasoil through fractionators (Fs), is fed into a second vacuum distillationunit (V2) to obtain a feedstock for high-quality lube base oil and theremaining amount of unconverted oil. The remaining amount of unconvertedoil, obtained from the second vacuum distillation unit (V2), isintroduced into a second hydrocracking unit (HDC2) to additionallyproduce diesel and light oil fractions, and then the produced diesel andlight oil fractions are recycled to the fractionators (Fs).

In the two-stage hydrocracking process (HDC1 and HDC2) according to thepresent invention, hydrocracking is carried out in two separatereactors, unlike the prior hydrocracking unit, which consists only of asingle stage. Thus, there are advantages in that the size of thereactors can be reduced, severity of operating conditions can bereduced, and the hydrocracking reaction can be easily controlled so asto maximize the production of diesel oil.

In general, because a one-through two-stage hydrocracking process isoperated at a low conversion rate, the content of polycyclic aromaticcomponents in the unconverted oil (UCO), which is a bottom oil fraction,is high, and the quality of the unconverted oil (UCO) is generallyinferior to that in the case in which the single-stage hydrocrackingprocess is used. For this reason, there is a problem in that theunconverted oil is difficult to use as a feedstock for high-quality lubebase oil. However, in the present invention, the recovery of therequired raw materials can be maximized by recycling the unconverted oil(UCO) through the two-stage hydrocracking process, and the reactionconversion rate can be increased by recycling the remaining unconvertedoil (UCO), thus improving the quality of the feedstock for high-qualitylube base oil. Also, the production of the feedstock for high-qualitylube base oil can be increased.

The hydrotreating process (HDT) is a process of removing sulfur,nitrogen, oxygen and metal components from the vacuum gas oil as afeedstock, and the hydrotreated vacuum gas oil is converted to lighthydrocarbons through a hydrocracking process in the first hydrocrackingunit (HDC1).

The light and heavy hydrocarbons, produced through the firsthydrocracking unit (HDC1), are fed into fractionators Fs to separatethem into oil products and unconverted oil (UCO). A portion of theseparated unconverted oil (UCO) is fed into a second vacuum distillationunit (V2) to separate a feedstock for high-quality lube base oil, havinga given viscosity grade, therefrom, and to recover the remaining amountof unconverted oil (UCO).

The remaining amount of unconverted oil from the second vacuumdistillation unit V2 is fed into a second hydrocracking unit (HDC2)together with the remaining unconverted oil resulting from thefractionators (Fs), and the light and heavy hydrocarbons producedthrough the second hydrocracking unit (HDC2) are recycled to thefractionators (Fs).

Herein, the ratio of the unconverted oil fed into the secondhydrocracking unit (HDC2) to the unconverted oil produced in thefractionators Fs is preferably 1:2-1:5, and the ratio of the unconvertedoil fed from the second vacuum distillation unit (V2) into the secondhydrocracking unit (HDC2) to the unconverted oil fed into the secondvacuum distillation unit (V2) is preferably 1:1.2-1:1.5.

The second vacuum distillation unit (V2) is operated at a bottomtemperature of 320-350° C., a bottom pressure of 140-160 mmHg, a toptemperature of 75-95° C. and a top pressure of 60-80 mmHg. The feedstockfor high-quality lube base oil having a given viscosity grade, obtainedin the second vacuum distillation unit (V2), can further be subjected toa dewaxing process and a stabilization process.

FIG. 2 is a schematic process diagram of an embodiment of the presentinvention, in which a feedstock for high-quality lube base oil isproduced in a fuel oil hydrocracking process in a recycle-mode operationusing a mixture of vacuum gas oil and coker gas oil as a feedstock.Referring to FIG. 2, in the present invention, atmospheric residue (AR),separated from a crude distillation unit (CDU), is distilled in a firstdistillation unit V1 to separate it into vacuum gas oil and vacuumresidue or a mixture (VR/AR) of vacuum residue (VR) and atmosphericresidue (AR). The vacuum gas oil (VGO) is fed directly to ahydrotreating unit HDT, and the vacuum residue (VR) or the atmosphericresidue/vacuum residue mixture (VR/AR) is passed through fractionators(Fs′), subjected to a coking process in coker drums, and then passedagain through the fractionators Fs′, thus obtaining coker gas oil (CGO).The coker gas oil (CGO) thus obtained is fed into a hydrocracking unitHDT together with the vacuum gas oil (VGO), and the two-stagehydrocracking process according to the present invention is carried out.

The process of producing the coker gas oil (CGO) will not be describedin further detail. The vacuum residue (VR) or the atmospheric oil/vacuumresidue mixture (VR/AR), separated from the first distillation unit(V1), is passed through the fractionators (Fs′) to separatelow-boiling-point components therefrom, and the remaining oil fractionis fed into coker drums and heated in the coker drums to a temperaturesufficient for forming coke. At this time, steam is also fed into thecoker drums in order to maintain the lowest speed and the shortestresidence time in the heater coils and to suppress the formation of cokein the heater coils. Liquid remaining in the coker drums is converted tocoke and light hydrocarbon gases, and all of the gases are dischargedthrough the top of the coker drums. In order to carry out this process,at least two coker drums are required. While coke is formed in one drum,the flow of oil to the other drum is blocked, and coke is removed fromthe other drum. The coker gas oil (CGO), produced through this cokingprocess, has poor color stability and a high content of HPNA (heavypoly-nuclear aromatic hydrocarbons) (having more than 7 aromatic rings),and for this reason, unconverted oil (UCO), produced by feeding thecoker gas oil to the hydrotreating and hydrocracking units, isunsuitable for use as a feedstock for high-quality lube base oil.

However, where unconverted oil (UCO) is recycled through the secondhydrocracking unit (HDC2) according to the method of the presentinvention, it is possible to secure high-quality unconverted oil (UCO)having a low HPNA content and ensured stability, and the production of100N- and 150N-grade feedstocks for high-quality lube base oil can bemaximized. In addition, coker gas oil (CGO), which has been used asBunker-C (B-C) oil or DSL oil, can be used as a raw material forproducing high-quality lube base oil, and thus the added value of theproduct can be increased, leading to an improvement in economicefficiency.

Specific conditions for the coking process in the method according tothe present invention are shown in Table 1 below.

TABLE 1 Operating conditions (unit) Range Heater discharge temperature(° C.) 480-500 Coker drum temperature (° C.) 500-600 Top-coker drumpressure (psig) 15-30 Recycling ratio, recycle volume/feed volume0.05-0.2 

The coker gas oil (CGO), produced from the coking process, is mixed withvacuum gas oil and fed into the hydrotreating unit HDT. When the contentof the vacuum gas oil in the mixture of the coker gas oil (CGO) with thevacuum gas oil (VGO) is increased, the production of a feedstock forhigh-quality lube base oil will be increased, but the production costwill be increased, and when the content of the coker gas oil (CGO) isincreased, the production cost will be advantageously reduced. However,because the properties of the coker gas oil (CGO) are inferior to thoseof the vacuum gas oil (VGO), the mixing volume ratio (VGO/CGO) betweenthe vacuum gas oil (VGO) and the coker gas oil (CGO) is preferably 2-9.

The coker gas oil (CGO), extracted from the vacuum residue (VR) or theatmospheric residue/vacuum residue mixture (VR/AR) in an amount of about20-50 vol %, can be mixed with the vacuum gas oil (VGO) and can be usedas a feedstock in the hydrotreating and hydrocracking units (HDT andHDC). Thus, when the same amount of atmospheric residue (AR) is fed intothe first distillation unit (V1), there is an advantage in that about10-50% of the atmospheric residue can be converted to high-value-addedlight oil and a feedstock for high-quality lube base oil, unlike thecase where only vacuum gas oil (VGO) is used as the feedstock in thefirst distillation unit (V1).

FIG. 3 is a schematic process diagram of an embodiment of the presentinvention, in which a feedstock for high-quality lube base oil isproduced in a fuel oil hydrocracking process in a recycle-mode operationusing a mixture of vacuum gas oil and deasphalted oil as a feedstock.Referring to FIG. 3, according to the present invention, atmosphericresidue (AR) is distilled in a first vacuum distillation unit V1 toseparate it into vacuum gas oil (VGO) and vacuum residue (VR). Thevacuum gas oil (VGO) is fed directly to a hydrotreating unit HDT, andthe vacuum residue (VR) is fed into a solvent deasphalting unit (SDA) toobtain deasphalted oil from which asphalt and impurities have beenremoved. The deasphalted oil (DAO) thus obtained is fed into thehydrotreating unit (HDT) together with the vacuum gas oil (VGO), and thetwo-stage hydrocracking reaction is carried out in the same manner asdescribed above.

The process of producing the deasphalted oil (DAO) will now be describedin further detail. The deasphalted oil (DAO) is produced by feeding thevacuum residue (VR), produced in the first vacuum distillation unit(V1), as a feedstock to the solvent deasphalting unit (SDA) so as tosuitably remove asphalt and impurities therefrom. As the solvent in thesolvent deasphalting unit (SDA), n- or iso-paraffin solvent having 3-6carbon atoms is mainly used. Specifically, the solvent is selected fromthe group consisting of n-propane, n-butane, isobutene, n-pentane andn-hexane. Also, the yield of the deasphalted oil (DAO) with respect tothe feedstock vacuum residue (VR) varies depending on the operatingconditions and the kind of solvent, shows a tendency to increase with anincrease in the carbon number of the solvent, and is generally about15-80%.

The deasphalted oil (DAO), produced in the solvent deasphalting process,has low metal and residual carbon content, but has a high aromaticcontent and contains an oil fraction having a high boiling point, andthus it is difficult to use as a feedstock for high-quality lube baseoil.

However, when the unconverted oil (UCO) is fed into the secondhydrocracking unit (HDC2) and recycled according to the method of thepresent invention, the aromatic content of the deasphalted oil can bereduced, and it is possible to remove the oil fraction having highboiling point, and thus the deasphalted oil can be used as a feedstockfor high-quality lube base oil. The use of such deasphalted oil (DAO)allows restriction on a feedstock for high-quality lube base oil to berelieved and the added value of the product to be increased, leading toan improvement in economic efficiency.

The deasphalted oil (DAO), extracted from the vacuum residue (VR) or theatmospheric residue/vacuum residue mixture (VR/AR) in an amount of about20-50 vol %, can be mixed with the vacuum gas oil (VGO) and can be usedas a feedstock in the hydrotreating and hydrocracking units (HDT andHDC). Thus, when the same amount of atmospheric residue (AR) is fed intothe first distillation unit (V1), there is an advantage in that about10-50% of the atmospheric residue can be converted to high-valued-addedlight oil and a feedstock for high-quality lube base oil, unlike thecase where only vacuum gas oil (VGO) is used as the feedstock in thefirst distillation unit (V1).

When the content of the vacuum gas oil in the mixture of the deasphaltedoil (DAO) with the vacuum gas oil (VGO) is increased, the production ofhigh-quality lube base oil will be increased, but the production costwill be increased, and when the content of the deasphalted oil (DAO) isincreased, the production cost will be advantageously reduced. However,because the properties of the deasphalted oil are inferior to those ofthe vacuum gas oil (VGO), the mixing volume ratio (VGO/DAO) between thevacuum gas oil (VGO) and the deasphalted oil (DAO) is preferably 2-9.

The typical properties of vacuum gas oil (VGO), coker gas oil (CGO) anddeasphalted oil (DAO), which are fed into the hydrocracking unit (HDT)according to the present invention, are shown in Table 2 below.

TABLE 2 Properties of feedstocks in hydrocracking unit VGO CGO DAOSpecific gravity 0.8660 0.8504 0.8686 Sulfur/nitrogen (wt ppm) 937/7501137/1614 2200/600 C7 insoluble substances (wt %) 0.35 0.05 0.01 Fe (wtppm) 1.1 1.0 1.4 Ni + V (wt ppm) 1.0 1.0 LT 1.0 Si (wt ppm) — 3.5 LT 1.0Distillation (ASTM D-86) Initial boiling point 324.8 207.0 266  5% 354.3249.2 33.9 10% 373.6 272.2 348 30% 412.0 314.5 438 50% 440.7 342.5 48870% 474.5 370.8 539 90% 529.6 405.5 604 95% 546.8 422.0 633 Finalboiling point 586.0 452.0 699

Hereinafter, the present invention will be described in further detailwith reference to examples, but the scope of the present invention isnot limited thereto.

EXAMPLE 1

Vacuum gas oil (VGO), separated from atmospheric residue (AR) as afeedstock in the first vacuum distillation unit (V1), had the propertiesshown in Table 2 above, and was hydrotreated in the hydrotreating unit(HDT) under conditions of an LHSV (Liquid Hourly Space Velocity) of3.881 hr⁻¹, a pressure of 2417 psig, a temperature of 389° C. and ahydrogen feed rate of 1374 Nm³/m³ using KF-848 (Albemarle) as acatalyst. The hydrotreated oil was treated in the first hydrocrackingunit (HDC1) under conditions of an LHSV of 1.068 hr⁻¹, a pressure of 170bar and a temperature of 395° C. using DHC-8 (UOP) as a catalyst at ahydrogen feed rate of 1050 nm³/m³, and was then passed through aconventional separator and a plurality of fractionators to recover someof the diesel and light oil products, having a boiling point of lessthan 410° C. Then, the remaining oil was treated in the secondhydrocracking unit (HDC2) together with the recycled UCO, describedbelow, under conditions of an LHSV of 1.613 hr⁻¹, a pressure of 170 barand a temperature of 403° C. using a DHC-8 catalyst (UOP) at a hydrogenfeed rate of 1028 nm³/m³. Then, the hydrocracked oil was passed througha conventional separator and a plurality of fractionators to recoverdiesel and light oil products, having a boiling point of 410° C., thusobtaining unconverted oil (UCO) having the properties shown in Table 2above. The obtained unconverted oil was subjected to vacuum distillationin a UCO vacuum distillation unit (V2) under conditions of a toppressure of 75 mmHg, a top temperature of 80° C., a bottom pressure of150 mmHg and a bottom temperature of 325° C., thus obtaining 20 LV %light distillate, a 32 LV % 100N distillate, 22 LV % middle distillate,4 LV % 150N distillate and 22 LV % bottom product, shown in Table 3below.

Among them, only the 100N and 150N distillates were drawn out asintermediate products in an amount of 36% (100N: 32% and 150N: 4%) basedon the feed amount (the amount of UCO fed into V2), and the remainingdistillates (64% of the feed amount) were combined and recycled to thesecond hydrocracking unit (HDC2). Thus, 100N- and 150N-grade feedstocksfor high-quality lube base oil, having a high viscosity index and 150Nand low volatility, as shown in Table 3 below, were produced. Also,because 36% of UCO was drawn out, the accumulation of refractorycomponents and poly-nuclear aromatic components were prevented, whilethe reaction conversion rate was increased, leading to an improvement inquality. In addition, the spare capacities of V1 and R1 were provided,and thus additional treatment capacity corresponding to the productionof the feedstock for lube base oil was provided, and thus it waspossible to use the system at very high efficiency.

TABLE 3 100N Middle 150N Bottom UCO Light distillate distillatedistillate distillate product Specific gravity 0.8289 0.7393 0.82230.8287 0.8349 0.8421 Distillation, ASTM D1160, @760 mmHg, ° C. Initialboiling point 220 227 368 387 406 412  5% 385 380 390 401 428 440 10%404 395 402 421 440 465 30% 426 402 424 444 467 478 50% 450 410 438 459482 496 70% 477 418 453 478 501 518 90% 535 426 471 503 521 541 95% 574433 480 512 542 578 Final boiling point 613 446 495 533 573 613Viscosity, cSt @40° C. 13.15 17.74 @ 100° C. 3.493 2.968 4.226 5.0656.653 7.523 Viscosity index 152 113 149 — — — Flash point (COC) ° C. 146230 243 266 289 Pour point 46 33 39 45 51

EXAMPLE 2

Vacuum residue (VR), separated from atmospheric residue (AR) as afeedstock in the first vacuum distillation unit (V1), was passed throughthe fractionators (Fs′) to separate some components having a low boilingpoint, and the remaining oil was heated to 500° C. and fed into cokerdrums. In the coker drums, the vacuum residue was heated underconditions of a temperature of 550° C. and a top coker drum pressure of25 psig, so that liquid remaining in the drums was converted to coke andlight hydrocarbon gases, and all of the gases were passed through thefractionators (Fs′) to separate them into LPG, gas, naphtha and cokergas oil (CGO).

The coker gas oil (CGO) and the vacuum gas oil (VGO) had the propertiesshown in Table 2, below, and were hydrocracked in the hydrocracking unit(HDT) under conditions of an LHSV of 3.56 hr⁻¹, a pressure of 2417 psig,a temperature of 384° C. and a hydrogen feed rate of 962 Nm³/m³ usingUF-210STARS (UOP) as a catalyst. The hydrocracked oil was treated in thefirst hydrocracking unit (HDC1) under conditions of an LHSV (LiquidHourly Space Velocity) of 1.246 hr⁻¹, a pressure of 170 bar and atemperature of 395° C. using UF-210STARS/DHC-32 (UOP) as a catalyst at ahydrogen feed rate of 1180 Nm³/m³, and then was passed through aconventional separator and a plurality of fractionators to recover somediesel and light oil products having a boiling point lower than 370° C.The hydrocracked oil was treated in the second hydrocracking unit (HDC2)together with the recycled UCO, described below, in conditions of anLHSV of 1.613 hr⁻¹, a pressure of 170 bar and a temperature of 398° C.using a DHC-8 catalyst (UOP) at a hydrogen feed rate of 1028 Nm³/m³.Then, the hydrocracked oil was passed through a conventional separatorand a plurality of fractionators to recover diesel and light oilproducts, having a boiling point lower than 370° C., thus obtainingunconverted oil (UCO) shown in Table 4 below. The obtained UCO wassubjected to vacuum distillation in the second vacuum distillation unit(V2) under conditions of a top pressure of 75 mmHg, a top temperature of80° C., a bottom pressure of 148 mmHg and a bottom temperature of 330°C., thus obtaining 30 LV % light distillate, 35 LV % 100N distillate, 18LV % middle distillate, 4 LV % 150N distillate and 13 LV % bottomproduct, as shown in Table 4 below.

Among them, only the 100N and 150N distillates were drawn out asintermediate products in an amount of 39% (that is, 100N: 35% and 150N:4%) based on the feed amount (the amount of UCO fed into V2), and theremaining distillates (61%) were combined and recycled to the secondhydrocracking unit (HDC2). Thus, 100N- and 150N-grade feedstocks forhigh-quality lube base oil, having high viscosity index and lowvolatility, as shown in Table 4, were produced, and because 39% of theUCO was drawn out, high-quality unconverted oil, having a lowpoly-nuclear aromatic component content and ensured stability, could besecured. Also, because additional treatment capacity corresponding tothe production of the feedstock for lube base oil was provided, thesystem could be very efficiently utilized. In addition, because cokergas oil (CGO), which has been used B-C oil or DSL oil, could be used asa raw material for producing high-quality lube base oil, the added valueof the feedstock could be increased, leading to an improvement ineconomic efficiency.

TABLE 4 Light 100N Middle 150N Bottom UCO distillate distillatedistillate distillate product Specific gravity 0.8250 0.7390 0.82230.8284 0.8348 0.8423 Distillation, ASTM D1160, @760 mmHg, ° C. Initialboiling point 225 227 365 381 403 410  5% 372 368 388 400 426 440 10%395 384 400 421 438 465 30% 416 402 422 444 466 478 50% 442 408 436 456482 498 70% 471 416 452 477 503 518 90% 530 424 470 498 521 539 95% 572431 479 510 543 579 Final boiling point 613 444 494 531 574 613Viscosity, cSt @40° C. 12.9 17.62 @ 100° C. 3.432 2.932 4.21 5.060 6.6527.526 Viscosity index 149 112 148 Flash point (COC) ° C. 142 222 240 264286 Pour point 42 33 39 45 51

EXAMPLE 3

Vacuum residue (VR), separated from atmospheric residue (AR) as afeedstock in the first vacuum distillation unit (V1), was fed into thesolvent deasphalting unit (SDA) to suitably remove asphalt andimpurities therefrom. Herein, as the deasphalting solvent, n-propane(N-C3) was used, and the deasphalted oil (DAO) was produced at a yieldof 39% at a pressure of 45.7 kg/cm²g and an asphaltene separationtemperature of 83° C. The vacuum gas oil (VGO) and the deasphalted oil(DAO), having the properties shown in Table 2 above, were fed into thehydrotreating unit (HDT) at a mixing volume ratio (VGO/DAO) of 3-5 andhydrocracked therein under conditions of an LHSV of 3.01 hr⁻¹, apressure of 2488 psig, a temperature of 395° C. and a hydrogen feed rateof 1125 Nm³/m³ using UF-210STARS (UOP) as a catalyst. The hydrotreatedoil was treated in the first hydrocracking unit (HDC1) under conditionsof an LHSV (Liquid Hourly Space Velocity) of a 1.208 hr⁻¹, pressure of a170 bar and temperature of a 405° C. using UF-210STARS/DHC-32 (UOP) as acatalyst at a hydrogen feed rate of 1250 Nm³/m³, and then passed througha conventional separator and a plurality of fractionators to recoversome of diesel and light oil products, having a boiling temperature of370° C. The hydrocracked oil was treated in the second hydrocrackingunit (HDC2) together with the recycled UCO, described below, underconditions of an LHSV of 1.405 hr⁻¹, a pressure of 170 bar and atemperature of 403° C. using a HC-215 catalyst (UOP) at a hydrogen feedrate of 1200 Nm³/m³. Then, the hydrocracked oil was passed through aconventional separator and a plurality of fractionators to recoverdiesel and light oil products, having a boiling point lower than 370°C., thus obtaining unconverted oil (UCO) having the properties shown inTable 5 below. The unconverted oil was fed into the vacuum distillationunit (V2), in which it was subjected to vacuum distillation underconditions of a top pressure of 70 mmHg, a top temperature of 80° C., abottom pressure of 150 mmHg and a bottom temperature of 345° C., thusobtaining 17 LV % light distillate, 30 LV % 100N distillate, 20 LV %middle distillate, 4 LV % 150N distillate and 29 LV % bottom product.

Among them, only the 100N and 150N distillates were drawn out asintermediate products in an amount of 34% (that is, 100N: 30% and 150N:4%) based on the feed amount (the amount of UCO fed into V2), and theremaining distillates (66%) were combined and recycled to the secondhydrocracking unit (HDC2). Thus, the 100N- and 150N-grade feedstocks forhigh-quality lube base oil, having high viscosity index and lowvolatility, as shown in Table 5 below, were produced. Also, because 34%of the UCO was drawn out, oil fractions, having a low poly-nucleararomatic component content and a high boiling point, could be removed,so that high-quality unconverted oil could be secured, and restrictionon feedstock oil was relieved, and thus the added value of the productcould be increased, leading to an improvement in economic efficiency.

TABLE 5 150N Bottom UCO Light distillate 100N distillate Middledistillate distillate product Specific gravity 0.8340 0.7390 0.82230.8284 0.8348 0.8423 Distillation, ASTM D1160, @760 mmHg, ° C. Initialboiling point 225 227 365 381 403 410  5% 372 368 388 400 427 450 10%395 384 400 421 443 472 30% 416 402 422 443 470 494 50% 458 408 436 455493 518 70% 529 413 452 476 510 549 90% 562 420 470 497 530 595 95% 598428 479 508 558 613 Final boiling point 699 440 494 529 589 699Viscosity, cSt @40° C. 12.9 17.62 @ 100° C. 3.432 2.918 4.21 5.05 6.809.082 Viscosity index 149 109 146 — — — Flash point (COC) ° C. 142 220239 264 301 Pour point 42 33 39 45 53

COMPARATIVE EXAMPLE

Vacuum gas oil (VGO), separated from atmospheric residue (AR) as afeedstock in the first vacuum distillation unit and having theproperties shown in Table 2, was treated in a hydrotreating unit underconditions of an LHSV (Liquid Hourly Space Velocity) of 3.429 hr⁻¹, apressure of 2397 psig and a temperature of 385.8° C. using UF-210STARS(UOP) as a catalyst at a hydrogen feed rate of 842 Nm³/m³. Thehydrotreated oil was treated in a hydrocracking unit together with therecycled UCO, described below, under conditions of an LHSV of 1.241hr⁻¹, a pressure of 2397 psig and a temperature of 395.2° C. using aUF-210/HC-115/UF-100 catalyst (UOP) at a hydrogen feed rate of 1180Nm³/m³.

Then, the hydrocracked oil was passed through a conventional separatorand a plurality of fractionators to recover diesel and light oilproducts, having a boiling point lower than 350° C., thus obtainingunconverted oil (UCO) having the properties shown in Table 6. Theunconverted oil was fed into a second vacuum distillation unit andsubjected to vacuum distillation therein under conditions of a toppressure of 75 mmHg, a top temperature of 80° C., a bottom pressure of150 mmHg and a bottom temperature of 325° C., thus obtaining 32.5 LV %light distillate, 34.8 LV % 100N distillate, 14.6 LV % middle productdistillate and 18.1 LV % bottom product 150N distillate.

Among them, only the 100N and 150N distillates were drawn out asintermediate products in an amount of 52.9% (that is, 100N: 34.8% and150N: 18.1%) based on the feed amount (the amount of the UCO fed intothe second vacuum distillation unit), and the remaining distillates(47.1% of the feed amount) were combined and recycled to a hydrocrackingprocess. Thus, the 100N- and 150N-grade feedstocks for high-quality lubebase oil, having high viscosity indexes and low volatilities, as shownin Table 6 below, were produced.

TABLE 6 Middle 150N UCO Light distillate 100N distillate distillatedistillate Specific gravity 0.8271 0.8374 0.8388 0.8418 0.8449Distillation, ASTM D1160, @760 mmHg, ° C. Initial boiling point 276 338401 412 437  5% 368 358 410 428 449 10% 398 362 412 434 453 30% 432 376418 443 461 50% 457 383 424 459 475 70% 485 392 432 478 496 90% 537 403447 503 531 95% 567 406 456 532 552 Final boiling point 590 414 471 533562 Viscosity, cSt @40° C. 20 19.39 @ 100° C. 4.428 2.978 4.305 5.0566.787 Viscosity index 136 113 132 — — Flash point (COC) ° C. 212 250Pour point 33 39

Although the preferred embodiment of the present invention has beendescribed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A method of producing a feedstock for high-quality lube base oil fromunconverted oil, the method comprising: distilling atmospheric residue(AR) in a first vacuum distillation process (V1) to obtain vacuum gasoil (VGO), and feeding the vacuum gas oil (VGO) into a hydrotreatingunit (HDT); removing impurities from the vacuum gas oil through thehydrotreating unit (HDT); obtaining light and heavy hydrocarbons fromthe vacuum gas oil through a first hydrocracking unit (HDC1); feedingthe light and heavy hydrocarbons into fractionators (Fs) to separate thehydrocarbons into oil products and unconverted oil; feeding a portion ofthe separated unconverted oil into a second vacuum distillation unit(V2) to obtain a feedstock for high-quality lube base oil, having agiven viscosity grade, and the remaining unconverted oil; feeding theremaining unconverted oil separated from the fractionators (Fs) and theunconverted oil obtained from the second vacuum distillation unit (V2)into a second hydrocracking unit (HDC2); and recycling light and heavyhydrocarbons, obtained through the second hydrocracking process (HDC2),to the fractionators (Fs).
 2. A method for producing a feedstock forhigh-quality lube base oil from unconverted oil, the method comprising:distilling atmospheric residue (AR) in a first vacuum distillationprocess (V1) to separate it into vacuum gas oil (VGO) and vacuum residue(VR) or a mixture of atmospheric residue (AR) with vacuum residue (VR),feeding the vacuum gas oil (VGO) directly into a hydrotreating (HDT)unit, feeding the vacuum residue (VR) or the vacuum residue/atmosphericresidue mixture (VR/AR) through fractionators (Fs′) to coker drums tosubject it to a coking process and passing the coked residue throughfractionators (Fs′) to obtain coker gas oil, and feeding the obtainedcoker gas oil together with the vacuum gas oil (VGO) into ahydrotreating (HDT) unit; removing impurities from the vacuum gas oiland the coker gas oil through the hydrotreating (HDT) unit; obtaininglight and heavy hydrocarbons from the vacuum gas oil through a firsthydrocracking (HDC1) unit; feeding the light and heavy hydrocarbons intofractionators (Fs) to separate the hydrocarbons into oil products andunconverted oil; feeding a portion of the unconverted oil to a secondvacuum distillation unit (V2) to obtain a feedstock for high-qualitylube base oil, having a given viscosity grade, and the remainingunconverted oil; feeding the remaining unconverted oil, separated fromthe fractionators, and the unconverted oil, obtained from the secondvacuum distillation unit (V2), into a second hydrocracking unit (HDC2);and recycling light and heavy hydrocarbons, obtained through the secondhydrocracking unit (HDC2), to the fractionators (Fs).
 3. A feedstock ofproducing a feedstock for high-quality lube base oil from unconvertedoil, the method comprising: distilling atmospheric residue in a firstvacuum distillation unit (V1) to separate it into vacuum gas oil (VGO)and vacuum residue (VR), feeding the vacuum gas oil (VGO) directly intoa hydrotreating unit (HDT), feeding the vacuum residue into a solventdeasphalting unit (SDA) to obtain deasphalted oil (DAO) from whichasphalt and impurities have been removed, and feeding the deasphaltedoil (DAO) together with the vacuum gas oil (VGO) into the hydrotreatingunit (HDT); removing impurities from the vacuum gas oil and thedeasphalted oil through the hydrotreating unit (HDT); obtaining lightand heavy hydrocarbons from the vacuum gas oil and the deasphalted oilthrough a first hydrocracking unit (HDC1); feeding the light and heavyhydrocarbons into fractionators (Fs) to separate the hydrocarbons intooil products and unconverted oil; feeding a portion of the separatedunconverted oil into a second vacuum distillation unit (V2) to obtain afeedstock for high-quality lube base oil, having a given viscositygrade, and the remaining unconverted oil; feeding the remainingunconverted oil, separated from the fractionators, and the unconvertedoil, obtained from the second vacuum distillation unit (V2), into asecond hydrocracking unit (HDC2); and recycling light and heavyhydrocarbons, obtained through the second hydrocracking unit (HDC2), tothe fractionators (Fs).
 4. The method of claim 2, wherein the mixingvolume ratio (VGO/CGO) between the vacuum gas oil (VGO) and the cokergas oil (CGO), which are fed into the hydrotreating unit (HDT), is 2-9.5. The method of claim 3, wherein the mixing volume ratio (VGO/DAO)between the vacuum gas oil (VGO) and the deasphalted oil (DAO), whichare fed into the hydrotreating unit (HDT), is 2-9.
 6. The method ofclaim 1, wherein the ratio of the unconverted oil fed into the secondhydrocracking unit HDC2 to the unconverted oil produced in thefractionators Fs is 1:2-1:5.
 7. The method of claim 2, wherein the ratioof the unconverted oil fed into the second hydrocracking unit HDC2 tothe unconverted oil produced in the fractionators Fs is 1:2-1:5.
 8. Themethod of claim 3, wherein the ratio of the unconverted oil fed into thesecond hydrocracking unit HDC2 to the unconverted oil produced in thefractionators Fs is 1:2-1:5.
 9. The method of claim 1, wherein the ratioof the unconverted oil fed from the second vacuum distillation unit (V2)into the second hydrocracking unit HDC2 to the unconverted oil fed intothe second vacuum distillation unit V2 is 1:1.2-1:1.5.
 10. The method ofclaim 2, wherein the ratio of the unconverted oil fed from the secondvacuum distillation unit (V2) into the second hydrocracking unit HDC2 tothe unconverted oil fed into the second vacuum distillation unit V2 is1:1.2-1:1.5.
 11. The method of claim 3, wherein the ratio of theunconverted oil fed from the second vacuum distillation unit (V2) intothe second hydrocracking unit HDC2 to the unconverted oil fed into thesecond vacuum distillation unit V2 is 1:1.2-1:1.5.